1. Field of the Invention
The present invention relates to a projection exposure method used when a mask pattern is transferred onto a substrate such as a wafer in a lithography step for manufacturing, for example, a semiconductor device, an image pick-up device (CCD and the like), and a liquid crystal display device and a thin film magnetic head and a projection exposure apparatus, and more particularly suitable used for a scan exposure type projection exposure apparatus such as step and scan system which comprises a correction mechanism for an image formation characteristic and scans a mask and a substrate in synchronization with a projection optical system to perform exposure.
2. Related Background Art
In the projection exposure apparatus which transfers a reticle pattern as a mask onto a wafer, a glass plate or the like coated with resist through a projection optical system, an exposure must be performed in a state where a high image formation characteristic is always kept. As one factor which exerts influence on the image formation characteristic, there has been thermal deformations of a reticle and optical elements of the projection optical system due to an irradiation of exposure light. In order to correct the change of the image formation characteristic resulting from the thermal deformation of the reticle by the exposure, various propositions have been heretofore made. For example, in Japanese Patent Application Laid-open No. Heisei 4(1992)-192317, a technology was proposed, in which the distribution of the quantity of deformation on a pattern plane of a reticle is computed, and the change of the image formation characteristic caused by this deformation is corrected either by driving parts of lens elements of the projection optical system toward an optical axis or by inclining them relative to the optical axis.
Furthermore, full-field type projection exposure apparatuses, that is, steppers, have been heretofore widely used. In order to perform a transfer for a reticle pattern of a large area with a high precision without increasing a size of the projection optical system, scan exposing type projection exposure apparatuses (scan type exposure apparatuses) such as a step and scan system in which the reticle and the substrate are exposed in synchronization with the projection optical system have been lately become of major interest. Also concerning the correction of the image formation characteristic due to irradiation of exposure light in this scan type exposure apparatus, a technology was proposed, in which the quantity of changes of the image formation characteristic of the projection optical system due to the irradiation is corrected by using the correction method employed in the case of the full-field type exposure apparatus, in Japanese Patent Application Laid-open No. Heisei 6(1994)-291016 and U.S. Pat. No. 5,721,608 related to this Japanese Patent Application Laid-open.
The correction method of the image formation characteristic of the scan type exposure apparatus uses almost the technology to which a system devised for the full-field type apparatus is applied. A correction method considering the change of the image formation characteristic of the whole of the apparatus which includes the reticle and the projection optical system particular to the scan type exposure apparatus, due to irradiation of exposure light, has not been existed.
However, an original pattern illustrated in the reticle used in the scan type exposure apparatus has a large area equal to that of the reticle for use in the full-field type exposure apparatus or an area larger than that. The entire surface of the original pattern is sequentially illuminated in a slit-shaped illumination region during the scan exposure. On the contrary, since the projection optical system is made to become a state where it is always irradiated in the slit-shaped illumination region asymmetrically, in a computing method concerning the quantity of the thermal deformation of the reticle and projection optical system and in a correction method of the corresponding image formation characteristic, the difference occurs naturally. Moreover, influences on the projected image formed on the wafer are different between the case of the thermal expansion of the reticle and the case of the thermal expansion of the projection optical system.
Furthermore, also in the full-field type projection exposure apparatus, the line width of the pattern to be subjected to a projection exposure has been recently finer more and more, and it has been required to correct the image formation characteristic more precisely.